Transition of neon from ground state to excited state

In summary, neon has a lowest excited energy at the 1(s^2)2(s^2)2(p^5)3(s^1) state with an excitation energy of approximately 16.9eV. The next energy state is at 1(s^2)2(s^2)2(p^5)3(p^1) with an excitation energy of 19eV. In Franck Hertz experiment with neon, the current decreases at every 19eV, but not at 17eV. This is likely due to the selection rules and conservation of angular momentum during collisions between electrons and neon atoms. The 19 eV transition has a higher probability of occurring because it does not
  • #1
popeadam
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Neon has lowest excited energy at 1(s^2)2(s^2)2(p^5)3(s^1) state. And the excitation energy is about 16.9eV.
And next energy is at 1(s^2)2(s^2)2(p^5)3(p^1) state. And the excitation energy is about 19eV.

In Franck Hertz experiment with Neon, current decrease at every 19eV, no 17eV.

Why 19eV? Why not 17eV?
Why neon can't go to the lowest excited state directly. They go to high excited state and transfer to lowest energy. Why?
 
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  • #2
popeadam said:
Neon has lowest excited energy at 1(s^2)2(s^2)2(p^5)3(s^1) state. And the excitation energy is about 16.9eV.
And next energy is at 1(s^2)2(s^2)2(p^5)3(p^1) state. And the excitation energy is about 19eV.

In Franck Hertz experiment with Neon, current decrease at every 19eV, no 17eV.

Why 19eV? Why not 17eV?
Why neon can't go to the lowest excited state directly. They go to high excited state and transfer to lowest energy. Why?

It's a good question .. I don't actually know the answer off-hand. My guess is that it has to do with angular momentum conservation during the collision. For the 19 eV transition (actually 18.71 eV), a neon electron gets excited from a 2p to a 3p orbital ... that means that the orbital angular momentum associated with that particular electron doesn't change ([itex]\Delta l=0[/itex]). Also, for that transition, the total angular momentum of the atom does not change ([itex]\Delta J=0[/itex]).

My guess is that those transitions have a higher probability of being excited than ones where there is a net transfer of angular momentum between the incident electron and the neon atom.

Note that there is a transition to a 1s22s22p53s1 state that also corresponds to
[itex]\Delta J=0[/itex] (the energy is 16.85 eV), however that means that the angular momentum of the excited electron has to change (i.e. [itex]\Delta l=-1[/itex]), which is also probably not very likely.

Anyway, I am not sure this explanation is completely correct .. for example, the angular momentum coupling in the excited states of rare gases does not follow simple L-S coupling rules if I remember correctly. However, I do think it is at least plausible. For reference, I used the table of Ne energy levels found http://physics.nist.gov/PhysRefData/Handbook/Tables/neontable5.htm" [Broken].
 
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  • #3
SpectraCat said:
It's a good question .. I don't actually know the answer off-hand. My guess is that it has to do with angular momentum conservation during the collision. For the 19 eV transition (actually 18.71 eV), a neon electron gets excited from a 2p to a 3p orbital ... that means that the orbital angular momentum associated with that particular electron doesn't change ([itex]\Delta l=0[/itex]). Also, for that transition, the total angular momentum of the atom does not change ([itex]\Delta J=0[/itex]).

My guess is that those transitions have a higher probability of being excited than ones where there is a net transfer of angular momentum between the incident electron and the neon atom.

Note that there is a transition to a 1s22s22p53s1 state that also corresponds to
[itex]\Delta J=0[/itex] (the energy is 16.85 eV), however that means that the angular momentum of the excited electron has to change (i.e. [itex]\Delta l=-1[/itex]), which is also probably not very likely.

Anyway, I am not sure this explanation is completely correct .. for example, the angular momentum coupling in the excited states of rare gases does not follow simple L-S coupling rules if I remember correctly. However, I do think it is at least plausible. For reference, I used the table of Ne energy levels found http://physics.nist.gov/PhysRefData/Handbook/Tables/neontable5.htm" [Broken].


Thank you. But ([itex]\Delta l=0[/itex]) is against the selection rules?
 
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  • #4
popeadam said:
Thank you. But ([itex]\Delta l=0[/itex]) is against the selection rules?

What selection rules? These are collisional excitations, not excitations due to absorption of EM radiation ... as far as I am aware, there are no selection rules, you just need to conserve angular momentum (and linear momentum and energy).

Furthermore, the selection rule for EM absorption would be that the TOTAL angular momentum quantum number for the atom would have to change by one ([itex]\Delta J=\pm 1[/itex]) ... that would certainly allow the orbital angular momentum change of an individual electron to be zero .. that is what I was trying to indicate by [itex]\Delta l=0[/itex] .. sorry if it was confusing.
 
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1. What is the ground state of neon?

The ground state of neon is the lowest possible energy state that an atom can exist in. In this state, the electrons are in their lowest energy levels and are in their most stable arrangement.

2. How does neon transition from ground state to excited state?

Neon transitions from ground state to excited state when it absorbs energy, either through collisions with other particles or through absorption of light. This causes the electrons to move to higher energy levels, resulting in an excited state.

3. What happens to neon in its excited state?

In its excited state, neon has higher energy levels for its electrons. This causes the electrons to be less tightly bound to the nucleus and can result in the emission of light as the electrons move back down to lower energy levels.

4. How long does neon stay in its excited state?

The length of time that neon stays in its excited state varies depending on the amount of energy absorbed and the specific energy levels that the electrons are in. Generally, neon stays in its excited state for a very short amount of time before emitting light and returning to its ground state.

5. What are some practical applications of neon's transition from ground state to excited state?

Neon's transition from ground state to excited state is used in many applications, including neon signs, fluorescent lights, and lasers. By controlling the energy levels of neon, scientists and engineers are able to create a variety of colors and light intensities for different purposes.

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